Mapping Mountains – Hill Reclassifications – 100m Twmpau

 

Pen y Parc (SH 590 750) – 100m Sub-Twmpau reclassified to 100m Twmpau

There has been a reclassification to the list of 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Parc (SH 590 750)

The criteria for the list that this reclassification applies to are: 

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Parc and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north and west and has the A545 road to its south-east, and has the town of Beaumaris towards the north-east. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 26m of drop, based on the 114m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated bwlch height of c 88m based on interpolation of 5m contouring between 85m – 90m that appear on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

Therefore, the reclassification of this hill from 100m Sub-Twmpau status is due to LIDAR analysis, resulting in a 113.0m summit height and an 82.8m bwlch height, with these values giving this hill 30.1m of drop, which is sufficient for it to be classified as a 100m Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pen y Parc 

OS 1:50,000 map:  114, 115

Summit Height:  113.0m (LIDAR) 

Summit Grid Reference:  SH 59003 75009 (LIDAR) 

Bwlch Height:  82.8m (LIDAR) 

Bwlch Grid Reference:  SH 58497 75660 (LIDAR) 

Drop:  30.1m (LIDAR) 

 

Myrddyn Phillips (March 2021)